Generator
    energy_source = Energy_Source (Electric only)
    fluid_box = Fluid Box
    horizontal_animation = Animation
    vertical_animation = Animation
    smoke = Smoke
    -- animation runs at least this fast (also corresponds to sound)
    min_perceived_performance = d(0.25)
    -- Performance / minPerceivedPerformance * performanceToSoundSpeedup gives activity value
    performance_to_sound_speedup = d(0.5)
    effectivity = double
    fluid_usage_per_tick = double
